Heat exchanger for a gas turbine engine

ABSTRACT

A heat exchanger apparatus for a gas turbine engine includes: a plurality of heat exchanger pipes, each pipe having first and second ends; wherein the heat exchanger pipes are disposed in a repeating pattern such that each heat exchanger pipe is joined to at least one other heat exchanger pipe.

BACKGROUND OF THE INVENTION

This invention relates generally to gas turbine engines and methods foroil cooling in such engines.

Gas turbine engines are commonly provided with a circulating oil systemfor lubricating and cooling various engine components such as bearings,gearboxes, electrical generators, and the like. In operation the oilabsorbs a substantial amount of heat that must be rejected to theexternal environment in order to maintain the oil at acceptabletemperatures. As engine designs evolve the amount of heat to be rejectedis increasing.

Known oil cooling systems for gas turbine engines typically include oneor more air-to-oil heat exchangers, referred to as “air cooled oilcoolers” or “ACOCs”, and may also include air-to-air heat exchangers.These heat exchangers can be heavy and have high drag, and can requirespecial inlet and outlet ducts and large, heavy brackets.

The high weight is attributable partially to the need with existingdesigns to use heavy, high-strength alloys and to designs in which thestructural and thermal functions are addressed separately. Furthermore,these heat exchangers are used in a challenging environment with hightemperatures and pressures that can cause low cycle fatigue (“LCF”)problems and high vibration levels that can cause high cycle fatigue(“HCF”) problems.

Accordingly, there is a need for a gas turbine engine heat exchangerhaving low weight, compact size and good strength and fatigue life.

BRIEF DESCRIPTION OF THE INVENTION

This need is addressed by the present invention, which provides a heatexchanger having a plurality of joined, mutually-supporting heatexchanger pipes.

According to one aspect of the invention, a heat exchanger apparatus fora gas turbine engine includes a plurality of heat exchanger pipes, eachpipe having first and second ends; wherein the heat exchanger pipes aredisposed in a repeating pattern such that each heat exchanger pipe isjoined to at least one other heat exchanger pipe.

According to another aspect of the invention, each heat exchanger pipeis joined to other heat exchanger pipes at two or more locations.

According to another aspect of the invention, each heat exchanger pipeis joined to other heat exchanger pipes at three locations.

According to another aspect of the invention, the joints betweenneighboring heat exchanger pipes are defined by mutually shared wallportions of the heat exchanger pipes.

According to another aspect of the invention, the apparatus furtherincludes a fluid manifold, wherein the first and second ends of eachheat exchanger pipe are connected in fluid communication with the fluidmanifold.

According to another aspect of the invention, the fluid manifoldincludes at least one inlet channel and at least one outlet channel, andthe first end of each heat exchanger pipe is connected to an inletchannel and the second end of each heat exchanger pipe is connected toan outlet channel.

According to another aspect of the invention, the inlet and outletchannels are spaced-apart from each other; each heat exchanger pipe hasa shallow S shape with first and second ends; the first end of each heatexchanger pipe is connected to the inlet channel; and the second end ofeach heat exchanger pipe is connected to the outlet channel.

According to another aspect of the invention, each heat exchanger pipeincludes a straight central portion and first and second end bends thatare curved opposite each other.

According to another aspect of the invention, the heat exchanger pipesare grouped in pairs, each pair of heat exchanger pipes being mutuallyjoined and forming an X shape.

According to another aspect of the invention, each heat exchanger pipehas at least one bend therein.

According to another aspect of the invention, each heat exchanger pipehas a shape including two spaced-apart, parallel legs interconnected bya transverse bridge.

According to another aspect of the invention, each leg includes a firstupright segment, an axial segment, and a second upright segment.

According to another aspect of the invention, the bridge of each heatexchanger pipe is joined to the leg of a neighboring heat exchangerpipe.

According to another aspect of the invention, the heat exchanger pipesare arranged in two spaced-apart rows, wherein the heat exchanger pipesof the rows are disposed mirror-images acute angles to a reference axis.

According to another aspect of the invention, the heat exchanger pipesof the first row are interlocked with the heat exchanger pipes of thesecond row.

According to another aspect of the invention, an exterior surface of atleast one of the heat exchanger pipes includes an area-increasingstructure.

According to another aspect of the invention, the area-increasingstructure is made from a material different from the at least one heatexchanger pipe.

According to another aspect of the invention, channels defined betweenthe heat exchanger pipes having an approximately constant flow areaalong a selected direction of flow.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing Figuresin which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engineincorporating a heat exchanger system constructed according to an aspectof the present invention;

FIG. 2 is perspective view of a single heat exchanger pipe constructedaccording to an aspect of the present invention;

FIG. 3 is a perspective view of two of the heat exchanger pipes shown inFIG. 2;

FIG. 4 is a perspective view of three of the heat exchanger pipes shownin FIG. 3;

FIG. 5 is a perspective view of an array of the heat exchanger pipesshown in FIG. 2;

FIG. 6 is a perspective view of two of the heat exchanger pipes shown inFIG. 2, in an alternative arrangement;

FIG. 7 is a perspective view of four of the heat exchanger pipes shownin FIG. 6;

FIG. 8 is a perspective view of an array of the heat exchanger pipesshown in FIG. 6;

FIG. 9 is a perspective view of two alternative heat exchanger pipesconstructed according to an aspect of the present invention;

FIG. 10 is a perspective view of four of the heat exchanger pipes shownin FIG. 9;

FIG. 11 is a perspective view of six of the heat exchanger pipes shownin FIG. 9;

FIG. 12 is a perspective view of an array of the heat exchanger pipesshown in FIG. 9; and

FIG. 13 is a schematic cross-sectional view of a heat transfer pipeincorporating area-increasing structures.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denotethe same elements throughout the various views, FIG. 1 depicts a gasturbine engine 10 incorporating a heat exchanger apparatus constructedaccording to an aspect of the present invention. while the illustratedexample is a high-bypass turbofan engine, the principles of the presentinvention are also applicable to other types of engines, such aslow-bypass, turbojet, etc. The engine 10 has a longitudinal center lineor axis 11 and an outer stationary annular casing 12 disposedconcentrically about and coaxially along the axis 11. The engine 10 hasa fan 14, booster 16, compressor 18, combustor 20, high pressure turbine22, and low pressure turbine 24 arranged in serial flow relationship. Inoperation, pressurized air from the compressor 18 is mixed with fuel inthe combustor 20 and ignited, thereby generating combustion gases. Somework is extracted from these gases by the high pressure turbine 22 whichdrives the compressor 18 via an outer shaft 26. The combustion gasesthen flow into a low pressure turbine 24, which drives the fan 14 andbooster 16 via an inner shaft 28. The engine 10 includes a bypass duct32 into which the fan 14 discharges.

The engine 10 includes a known type of system for circulatingpressurized oil to various parts of the engine (for example, bearings)for lubrication and cooling. In operation, the oil absorbs a significantheat load which must then be rejected to the external environment. Thepresent invention provides a heat exchanger apparatus for cooling thatoil or other fluid. Generally stated, the heat exchanger includes aplurality of slender heat exchanger pipes which are exposed to a coolingair flow, and through which the oil is circulated. The pipes areconnected to each other to form a mutually self-supporting structure.Numerous physical configurations of the heat exchanger pipes arepossible. Several examples will be discussed in detail below.

FIGS. 2-5 illustrate an exemplary heat exchanger 40. More specifically,FIGS. 2-4 illustrate portions of the heat exchanger 40 in various stagesof assembly, while FIG. 5 illustrates the complete heat exchanger 40.

The heat exchanger 10 includes a fluid manifold 42 which is configuredto receive a fluid (e.g. lubrication oil or another liquid, or a gas) tobe cooled from the engine 10, circulate it through a plurality of heatexchanger pipes (described below), and return the cooled fluid to bestored or used by the engine 10. In the illustrated example, the fluidmanifold 42 is shown as including one or more inlet channels 44 and oneor more outlet channels 46 configured as side-by-side tubes.

The heat exchanger 40 includes a plurality of heat exchanger pipes 48which in operation are positioned to be exposed to a flow of coolingfluid (e.g., air), depicted by arrow “F”. For example, the heatexchanger 40 could be positioned with the heat exchanger pipes 48exposed within the bypass duct 32 (see FIG. 1). In general, in theembodiments shown in FIGS. 2-8, the bulk direction of the cooling fluidflow F is parallel to a first axis or direction “A” of the fluidmanifold 12, and perpendicular to a second axis or direction “B” of thefluid manifold 42, wherein axes A and B are mutually perpendicular toeach other.

Referring specifically to FIG. 2, each heat exchanger pipe 40 is arelatively long slender tube with at least one bend in it. As a generalprinciple it may be stated that for each bend added to a pipe, heattransfer capability is improved, while vibrational degree of freedom(“DOF”) is also increased. In the illustrated example, the heatexchanger pipe 40 is a single continuous member, but for convenience maybe described as having several segments. In particular, each heatexchanger pipe has two identical, spaced apart “legs” 50 which aregenerally parallel to each other. Each leg 50 has a first end 52 and asecond end 54, and the second ends 54 are connected by abridge 56 whichextends transversely between the two legs 50. Beginning at the first end52, each leg 50 includes a first upright segment 58, an axial segment60, and a second upright segment 62. The entire structure may bedescribed as having a shape similar to a “chair frame”. The first end 52of one leg 50 (also representing one terminal end of the entire heatexchanger pipe 48) is coupled in fluid communication with the inletchannel 44, and the first end 52 of the second leg 50 (also representinga second terminal end of the entire heat exchanger pipe) is coupled influid communication with the outlet channel 46. Optionally, multipleheat exchanger pipes 48 could be interconnected with each other, forexample using U-bends (not shown) so as to make multiple passes beforeterminating at the fluid manifold 42. Similarly, multiple heat exchangerpipes 48 could be arranged to provide pipe-to-pipe flow in a directionalong reference axis B, in which case some or all of the fluid manifold42 could be eliminated.

A single heat exchanger pipe 48 is relatively flexible and could besubject to damage from vibration loads resulting from engine operationor flow-induced vibrations caused by the aerodynamic shedding of theexternal air flow, commonly referred to as “fretting”. To counter this,multiple heat exchanger pipes 48 may be assembled contacting each otherat multiple locations so that they can mutually support each other,providing additional stiffness which raises the natural frequenciesabove the forcing frequency.

For example, in FIG. 3 the fluid manifold 42 is shown including twoinlet channels 44, 44′ respectively, and one outlet channel 46. One heatexchanger pipe 48 is connected to the first inlet channel 44 and theoutlet channel 46, and the second heat exchanger pipe 48′ is connectedto the outlet channel 46 and the second inlet channel 44′. Referring toa reference axis B parallel to the inlet channels 44, 44′, the two heatexchanger pipes 48, 48′ are in approximately the same axial position butare laterally offset from one another. The bridge 56 of the first heatexchanger pipe 48 is shown contacting to a first leg 50′ of the secondheat exchanger pipe 48′. The two heat exchanger pipes 48, 48′ are joinedto each other at the contact point.

As used herein in referring to the heat exchanger pipes 48, the term“joined” implies a solid, rigid structural connection of a permanentnature between the two joined elements. For example, the heat exchangerpipes 48 may be made separately and then joined using a known bondingprocess such as welding or brazing or diffusion bonding. Alternatively,the heat exchanger pipes 48 could be made as part of an integral,unitary, or monolithic whole, where the walls of the pipes are shared atthe contact points.

FIG. 4 shows a further stage of assembly where a third heat exchangerpipe 48″ has been added, connected to the first inlet channel 44 and theoutlet channel 46, and laterally in-line with the first heat exchangerpipe 48 and axially offset therefrom. Each leg 50 of the first heatexchanger pipe 48 contacts the corresponding leg 50″ of the third heatexchanger pipe 48″. In this arrangement the first heat exchanger pipe 48is contacted by and joined to other heat exchanger pipes 48′, 48″ atthree locations.

Finally, FIG. 5 depicts the heat exchanger 40 where the arrangement ofheat exchanger pipes 48 shown in FIG. 4 is repeated in both axial andlateral directions, and each heat exchanger pipe 48 is contacted by andjoined to other heat exchanger pipes at three locations. Thisarrangement provides significant additional stiffness and strength toeach of the heat exchanger pipe 48. Stated another way, the heatexchanger pipes 48 are mutually self-supporting. This gives the heatexchanger 40 good strength and stiffness so that its natural frequenciescan be made appropriately high, while still being light weight. Thisconfiguration is advantageous as compared to the prior art use of tieplates or struts to stiffen heat exchanger tubes. The heat exchangerpipes 48 may also be described as being “interlocked”. It is noted thatthe individual heat exchanger pipes 48 need not be joined or interlockedwith immediately neighboring heat exchanger pipes 48 in order toaccomplish the mutual self-support effect. For example, a first heatexchanger pipe 48 could be configured to joint or interlock with anotherheat exchanger pipe 48 that is separated from the first heat exchangerpipe 48 by one or more intervening heat exchanger pipes 48. This is truefor all of the embodiments described herein.

FIGS. 6-8 illustrate an alternative heat exchanger 140. Morespecifically, FIGS. 6 and 7 illustrate portions of the heat exchanger140 in various stages of assembly, while FIG. 8 illustrates the completeheat exchanger 140.

The heat exchanger 140 uses the heat exchanger pipes 148 which may beidentical to the heat exchanger pipes 48 as seen in FIGS. 2-5, butarranged in a different pattern. The heat exchanger 140 includes a fluidmanifold 142 comprising two pairs of channels, 143A and 143B, Eachchannel pair 143A, 143B includes one inlet channel 144 and one outletchannel 146, configured as side-by-side tubes. The pairs 143A and 143Brun parallel to each other and are laterally separated by a space 145.

The heat exchanger pipes 148 are oriented with a line running throughtheir ends 152 set at an acute angle to a reference axis B. A first end152 of one leg 150 (also representing one terminal end of the entireheat exchanger pipe) is coupled in fluid communication with the inletchannel 144 of the first pair 143A, and the first end 152 of the secondleg 150 (also representing a second terminal end of the entire heatexchanger pipe 148) is coupled in fluid communication with the outletchannel 146 of the first pair 143A.

A row of heat exchanger pipes 148 oriented as described above aredisposed along the first pair 143A of channels. Each heat exchanger pipe148 contacts and is joined to its neighboring heat exchanger pipe 148 inthe row at one location.

Another row of heat exchanger pipes 148′ are disposed along the secondpair 143B of channels, and arranged similarly, but are oriented as amirror-image to the first row of heat exchanger pipes 148 (in otherwords, they are angled opposite relative to the axis B). Each heatexchanger pipe 148′ contacts and is joined to its neighboring heatexchanger pipe 148′ in the row at one location.

As seen in FIG. 8, the heat exchanger pipes 148, 148′ of the two pairs143A, 143B are interwoven with each other so that each heat exchangerpipe 148, 148′ is contacted by and joined to other heat exchanger pipes148, 148′ at three locations.

FIGS. 9-12 illustrate an alternative heat exchanger 240. Morespecifically, FIGS. 9-11 illustrate portions of the heat exchanger 240in various stages of assembly, while FIG. 12 illustrates the completeheat exchanger 240.

The heat exchanger 240 includes a fluid manifold. In the illustratedexample, the fluid manifold includes an inlet channel 244 spaced-apartfrom an outlet channel 246.

The heat exchanger 240 includes a plurality of heat exchanger pipes 248which in operation are positioned to be exposed to a flow of coolingfluid (e.g. air), depicted by arrow “F”. In general, in the embodimentshown in FIGS. 9-12, the bulk direction of the cooling fluid flow F isparallel to a first axis or direction “A” of the fluid manifold, andperpendicular to a second axis or direction “B” of the fluid manifold,wherein axes A and B are mutually perpendicular to each other.

Referring specifically to FIG. 9, each heat exchanger pipe 248 is arelatively long slender tube with first and second ends 252, 254.Between the ends 252, 254, the heat exchanger pipe 248 has a straightcentral portion 256 with first and second end bends 258, 260 that arecurved opposite each other. The complete heat exchanger pipe 248 can bedescribed as having a shallow “S” shape. The first end 252 is coupled influid communication with the inlet channel 244, and the second end 254is coupled in fluid communication with the outlet channel 246.

Each heat exchanger pipe 248 is paired with a neighboring heat exchangerpipe 248 contacting and mutually joined at one point and forming an “X”shape. As seen in FIGS. 10 and 11, these pairs can be repeated in axialand lateral directions. Finally, FIG. 12 depicts the complete heatexchanger 240.

The heat exchanger pipes described above may be made from a material \suitable thermal conductivity and strength at expected operatingtemperatures. Nonlimiting examples of suitable materials includealuminum alloys, high-strength steels, and nickel-based alloys (e.g.INCONEL).

In any of the configurations described above, the heat exchanger pipesmay be configured such that the open spaces or flow channels for fluidflow between them are generally constant. Stated another way, the areaof each of the open spaces is approximately the same for any givenlocation along the direction of flow F. This avoids repeated expansionsor contractions in flow area that would create a substantial pressureloss.

All or part of the heat exchangers described above, including themanifolds and/or the heat exchanger pipes, or portions thereof, may bepart of a single unitary, one-piece, or monolithic component, and may bemanufactured using a manufacturing process which involves layer-by-layerconstruction or additive fabrication (as opposed to material removal aswith conventional machining processes). Such processes may be referredto as “rapid manufacturing processes” and/or “additive manufacturingprocesses,” with the term “additive manufacturing process” being termherein to refer generally to such processes. Additive manufacturingprocesses include, but are not limited to: Direct Metal Laser Sintering(DMLS), Direct Metal Laser Melting (DMLM), Laser Net Shape Manufacturing(LNSM), electron beam sintering, Selective Laser Sintering (SLS), 3Dprinting, such as by inkjets and laserjets, Sterolithography (SLS),Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), andDirect Metal Deposition (DMD).

Alternatively, portions of the heat exchangers described above could bemade by processes such as rolling, extruding, casting, or machining fromblanks, or by using an additive manufacturing process, and then bondedtogether, for example using known welding or brazing methods, ordiffusion bonding.

A significant feature of all of the heat exchanger configurationsdescribed above is that the air flow spaces between the heat exchangertubes are of approximately uniform size. A constant air flow areaminimizes pressure drop by reducing irreversible flow losses associatedwith flow acceleration and deceleration. While the exemplary figuresshow this is achieved using a repeatable tubular pattern, this is not alimiting feature of the invention. The same constant air flow space canbe achieved through a combination of changing the number of heatexchanger pipes and the shapes of the heat exchanger pipes along the airflow path. Such an arrangement results in a non-uniform distribution ofheat exchanger pipes and pips sizes, while maintaining a uniform airflow area. Manufacturing techniques such as additive manufacturingallows realization of such designs.

The exterior surfaces of any of the heat exchanger pipes described abovemay be provided with area-increasing structures to enhance the air-sideheat transfer. Nonlimiting examples of area-increasing structuresinclude fins, ribs, pin fins, grooves, and dimples. FIG. 13 shows ashort section of a heat transfer pipe 48 having a pipe wall 51 with anexterior surface 53. An array of spaced-apart annular fins 57 extendoutward from the exterior surface 53. The fins 57 or otherarea-increasing structure could be part of an integral, unitary ormonolithic construction with the pipe wall 51, for example being made bya conventional machining or additive machining process, or they could bemanufactured separately and then attached to the pipe wall 51. The fins57 or other area-increasing structure could be of the same material asthe pipe wall 51 or a different material.

The invention described herein has several advantages over the priorart. The integrated structural-thermal design allows for improvedLCF/HCF life, and improved heat exchanger packaging. For a given set oftemperature and pressure conditions, it can allow the use of a materialwith higher thermal conductivity and lower strength than would otherwisebe required. For example, depending on the specific application, itmight allow a nickel-based alloy to perform where no alloy wouldotherwise be suitable, or allow the substitution of a steel alloy inplace of a nickel alloy, or allow the substitution of an aluminum alloyin place a steel alloy.

The foregoing has described a heat exchanger apparatus. All of thefeatures disclosed in this specification (including any accompanyingclaims, abstract and drawings), and/or all of the steps of any method orprocess so disclosed, may be combined in any combination, exceptcombinations where at least some of such features and/or steps aremutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

What is claimed is:
 1. A heat exchanger apparatus for a gas turbineengine, comprising a plurality of heat exchanger pipes, each pipe havingfirst and second ends; wherein the heat exchanger pipes are disposed ina repeating pattern such that each heat exchanger pipe is joined to atleast one other heat exchanger pipe.
 2. The apparatus of claim 1 whereineach heat exchanger pipe is joined to other heat exchanger pipes at twoor more locations.
 3. The apparatus of claim 1 wherein each heatexchanger pipe is joined to other heat exchanger pipes at threelocations.
 4. The apparatus of claim 1 wherein the joints betweenneighboring heat exchanger pipes are defined by mutually shared wallportions of the heat exchanger pipes.
 5. The apparatus of claim 1further comprising a fluid manifold, wherein the first and second endsof each heat exchanger pipe are connected in fluid communication withthe fluid manifold.
 6. The apparatus of claim 5 wherein the fluidmanifold includes at least one inlet channel and at least one outletchannel, and the first end of each heat exchanger pipe is connected toan inlet channel and the second end of each heat exchanger pipe isconnected to an outlet channel.
 7. The apparatus of claim 5 wherein: theinlet and outlet channels are spaced-apart from each other; each heatexchanger pipe has a shallow S shape with first and second ends; thefirst end of each heat exchanger pipe is connected to the inlet channel;and the second end of each heat exchanger pipe is connected to theoutlet channel.
 8. The apparatus of claim 7 wherein each heat exchangerpipe includes a straight central portion and first and second end bendsthat are curved opposite each other.
 9. The apparatus of claim 7 whereintire heat exchanger pipes are grouped in pairs, each pair of heatexchanger pipes being mutually joined and forming an X shape.
 10. Theapparatus of claim 1 wherein each heat exchanger pipe has at least onebend therein.
 11. The apparatus of claim 1 wherein each heat exchangerpipe has a shape including two spaced-apart, parallel legsinterconnected by a transverse bridge.
 12. The apparatus of claim 11wherein each leg includes a first upright segment, an axial segment, anda second upright segment.
 13. The apparatus of claim 12 wherein thebridge of each heat exchanger pipe is joined to the leg of a neighboringheat exchanger pipe.
 14. The apparatus of claim 11 wherein the heatexchanger pipes are arranged in two spaced-apart rows, wherein the heatexchanger pipes of the rows are disposed mirror-images acute angles to areference axis.
 15. The apparatus of claim 13 wherein the heat exchangerpipes of the first row are interlocked with the heat exchanger pipes ofthe second row.
 16. The apparatus of claim 1 wherein an exterior surfaceof at least one of the heat exchanger pipes includes an area-increasingstructure.
 17. The apparatus of claim 16 wherein the area-increasingstructure is made from a material different from the at least one heatexchanger pipe.
 18. The apparatus of claim 1 wherein flow channelsdefined between the heat exchanger pipes having an approximatelyconstant flow area along a selected direction of flow.